In modern petrochemical engineering, ethylene and propylene are the most crucial basic materials. Ethylene can be used in preparing downstream products including polyethylene, styrene, vinyl acetate, ethylene oxide, and ethylene glycol, and the like. Propylene can be used in preparing downstream products including polypropylene, acrylonitrile, propylene oxide, and isopropyl alcohol, and the like. Ethylene and propylene and downstream products thereof are widely used in the fields of industry and agriculture, transportation, and national defense.
In recent years, the demand for ethylene and propylene remains high. Under the circumstance that oil resource gradually decreases, the short supply of oil in China can be greatly relieved through coal chemical technology, with which ethylene and propylene can be prepared from non-oil resource. This is significant in promoting the development of the national heavy chemical industry. Based on the coal chemical technology, methanol can be prepared from coal, and then olefins can be prepared from methanol.
At present, an apparatus for preparing olefins from methanol is similar to a catalytic cracking device, both being continuous reaction-regeneration type. According to patent literature U.S. Pat. No. 6,166,282, a process and a reactor for converting oxides to low carbon olefins are disclosed. A fast fluidized bed reactor is used in the above patent literature. Gas reacts in a reaction zone with low gas velocity, and then rises to a fast separation zone with rapidly decreasing inner diameter. Catalysts entrained in product are separated through a preliminary cyclone. Because the product and the catalysts are separated rapidly, secondary reaction can be effectively prevented. The reactor used in the above patent literature is an upflow fast fluidized bed reactor with a traditional feed inlet.
Chinese patent literature CN103121901A recites a method for converting oxygenated chemicals to generate low-carbon olefins. According to the above method, to-be-generated catalysts and regenerated catalysts are premixed in a catalyst blender, and then enter a reactor, thereby the problems of undermixing of catalysts and low yield of low-carbon olefins in a reaction zone in the prior art can be solved.
Chinese patent literature CN101164685A relates to a combined quick fluidized bed reactor for methyl alcohol or dimethyl ether catalytic reaction. According to the above patent literature, a separation device in a settling zone is arranged externally, so that space occupied by the settler can be reduced, thereby a settling velocity of catalysts can be increased, and residence time of olefins can be reduced. In the meantime, problems of low selectivity and low yield of ethylene and propylene can also be solved. As compared with a traditional quick fluidized bed reactor with external settler, the yield of ethylene can be increased by 4% and that of propylene can be increased by 3%.
In the prior art, in order to improve the settling separation effect of catalysts, the settler is structured with large size and large inner space. However, in this case, gas flow velocity in the settler is relatively small, causing long residence time of gas inside the settler. Consequently, secondary reaction of product with entrained catalysts would easily occur. The product finally obtained would therefore contain a lot of impurities, which is quite adverse to the preparation of olefins and aromatic hydrocarbons.